diff options
Diffstat (limited to 'vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go')
| -rw-r--r-- | vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go | 44 |
1 files changed, 35 insertions, 9 deletions
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go index 3d2e426..bc196b1 100644 --- a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go +++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go @@ -1,6 +1,6 @@ // Copyright 2017, The Go Authors. All rights reserved. // Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE.md file. +// license that can be found in the LICENSE file. // Package diff implements an algorithm for producing edit-scripts. // The edit-script is a sequence of operations needed to transform one list @@ -12,6 +12,13 @@ // is more important than obtaining a minimal Levenshtein distance. package diff +import ( + "math/rand" + "time" + + "github.com/google/go-cmp/cmp/internal/flags" +) + // EditType represents a single operation within an edit-script. type EditType uint8 @@ -112,6 +119,8 @@ func (r Result) Similar() bool { return r.NumSame+1 >= r.NumDiff } +var randBool = rand.New(rand.NewSource(time.Now().Unix())).Intn(2) == 0 + // Difference reports whether two lists of lengths nx and ny are equal // given the definition of equality provided as f. // @@ -177,6 +186,11 @@ func Difference(nx, ny int, f EqualFunc) (es EditScript) { // approximately the square-root of the search budget. searchBudget := 4 * (nx + ny) // O(n) + // Running the tests with the "cmp_debug" build tag prints a visualization + // of the algorithm running in real-time. This is educational for + // understanding how the algorithm works. See debug_enable.go. + f = debug.Begin(nx, ny, f, &fwdPath.es, &revPath.es) + // The algorithm below is a greedy, meet-in-the-middle algorithm for // computing sub-optimal edit-scripts between two lists. // @@ -194,20 +208,26 @@ func Difference(nx, ny int, f EqualFunc) (es EditScript) { // frontier towards the opposite corner. // • This algorithm terminates when either the X coordinates or the // Y coordinates of the forward and reverse frontier points ever intersect. - // + // This algorithm is correct even if searching only in the forward direction // or in the reverse direction. We do both because it is commonly observed // that two lists commonly differ because elements were added to the front // or end of the other list. // - // Running the tests with the "cmp_debug" build tag prints a visualization - // of the algorithm running in real-time. This is educational for - // understanding how the algorithm works. See debug_enable.go. - f = debug.Begin(nx, ny, f, &fwdPath.es, &revPath.es) - for { + // Non-deterministically start with either the forward or reverse direction + // to introduce some deliberate instability so that we have the flexibility + // to change this algorithm in the future. + if flags.Deterministic || randBool { + goto forwardSearch + } else { + goto reverseSearch + } + +forwardSearch: + { // Forward search from the beginning. if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 { - break + goto finishSearch } for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ { // Search in a diagonal pattern for a match. @@ -242,10 +262,14 @@ func Difference(nx, ny int, f EqualFunc) (es EditScript) { } else { fwdFrontier.Y++ } + goto reverseSearch + } +reverseSearch: + { // Reverse search from the end. if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 { - break + goto finishSearch } for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ { // Search in a diagonal pattern for a match. @@ -280,8 +304,10 @@ func Difference(nx, ny int, f EqualFunc) (es EditScript) { } else { revFrontier.Y-- } + goto forwardSearch } +finishSearch: // Join the forward and reverse paths and then append the reverse path. fwdPath.connect(revPath.point, f) for i := len(revPath.es) - 1; i >= 0; i-- { |